1. Field of the Invention
The present invention relates to bit mounting devices for mounting tool bits, such as driver bits and socket bits, to spindles of rotary tools, such as power screwdrivers.
2. Description of the Related Art
Japanese Laid-Open Utility Model Publication No. 3-59163, Japanese Laid-Open Patent Publication No. 2005-528991 (corresponding to WO03/103901), and Japanese Patent No. 3479936 teach techniques relating to bit mounting devices for mounting tool bits to spindles of tool bodies. The tool bits used in these techniques are attached to the spindles by magnetic forces and are called “magnetic connecting bits.”
According to the technique disclosed in Japanese Utility Model Publication No. 3-59163, a magnet is disposed at the bottom of a bit receiving hole and is biased in a bit removing direction by a spring. A stop ring is attached to the inner circumferential surface of the inlet portion of the bit receiving hole. The tool bit is prevented from being removed from the bit mounting hold due to direct engagement of the tool bit with the stop ring (called “stop ring engaging system”). With this arrangement, it is possible to prevent the magnet from being accidentally damaged.
According to the technique disclosed in Japanese Laid-Open Patent Publication No. 2005-528991, a bit mounting device has a magnet disposed at the bottom of a bit receiving hole for attracting and holding the bit. A steel ball(s) directly engages the outer circumferential surface of the tool bit in order to prevent the bit from being removed (called “steel ball engaging system”).
According to the technique of Japanese Patent No. 479936, a magnet is positioned within a hexagonal hole formed in a socket bit, so that a head of a hexagonal bolt can be attracted and can be held in position. However, this technique does not have direct relation with the construction for mounting the tool bit itself.
According to the stop ring engaging system of Japanese Utility Model Publication No. 3-59163, the tool bit is prevented from being removed by the engagement by the stop ring in addition to the attraction by the magnet. Therefore, in particular when the bit is removed, it is necessary for a user to pinch the bit with his or her fingers and to withdraw the bit by a large force for enlargement of the stop ring against the resilient force. Therefore, there has been a need for improvement in the operability for the bit removing operation.
Japanese Laid-Open Patent Publication No. 2005-528991 (corresponding to WO03/103901) is improved in the operability for the bit removing and mounting operations, because axially moving an operation sleeve can release the engagement by the steel ball(s) to enable removal of the tool bit against only the attracting force of the magnet. However, in the case of the steel ball engaging system, the mounting device must have a large diameter, because it is necessary to position the steel ball(s) around the tool bit. If the diameter of the mounting device is too large, magnetic connecting bits of the stopper ring engaging system that is most popularly incorporated cannot be used.
Therefore, there has been a need for bit mounting devices that enables tool bits to be easily removed without incorporating the steel ball engaging system.